Purpose: :
The clinical presentations and features of several disordersthat are due to presumed inflammation of the optic nerve sheath(perineuritis) are similar to optic neuritis, but perineuritisis not associated with development of MS and may require systemicinvestigation. We hypothesized that MRI features can differentiatebetween the two disorders.

Methods: :
During the period from 2004-2008, we diagnosed 10 patients withoptic perineuritis and 170 patients with typical optic neuritis(18-50 yrs). We reviewed the records for presenting symptoms(including pain on eye movement), clinical signs, age, gender,visual acuity, mean deviation for 24-2 Humphrey (MD in db),and optic disc features. We evaluated fat suppressed gadoliniumenhanced T1-weighted and short tau inversion recovery (STIR)orbital MRI in all patients for presence of abnormal enhancementof the optic nerve or of the optic nerve sheath alone, and abnormalsignal in the optic nerve.

Results: :
For perineuritis patients, the average age was 34 yrs (range:12-48 yrs); 9 were females; at presentation 8 had visual acuity≥ 20/40; 5 had optic disc swelling; 9 had pain on eye movement,and MD ranged from -1.3 to -31 db. Treatment with intravenousmethylprednisolone or high dose oral prednisone, followed bya gradual withdrawal, normalized the visual acuity and visualfield in 5/7 patients. The visual acuity, but not the field,improved in 1; and 1 had progressive vision loss despite highdose steroid therapy. In 3 patients without vision loss, painresolved with oral nonsteroidal anti-inflammatory agents. Allperineuritis eyes (none unaffected eyes) showed abnormal enhancementof the optic nerve sheath but not of the optic nerve. Abnormaloptic nerve signal on STIR occurred in 2. No perineuritis patientshad abnormal signal of brain white matter. No optic neuritispatients had abnormal enhancement of the optic nerve sheathalone.